1. Field of Invention
The invention relates to an ink ribbon feed mechanism for a thermal recording type printing apparatus used in a facsimile machine and the like.
2. Description of Related Art
In a facsimile apparatus, which is but one example of a thermal recording type printing apparatus, an ink ribbon for recording is placed in the path of travel of the recording paper (generally, ordinary paper). The ink ribbon is usually wound on a feed roll and printing is performed while the ink ribbon is being taken up onto a take-up roll. The ink ribbon is held stretched between the feed roll and the take-up roll. Across the ink ribbon are oppositely arranged the recording paper and a recording head. With the heating of the recording head, the ink coated on the ink ribbon melts to be transferred onto the recording paper.
FIG. 9 is a plan view showing an ink ribbon feed mechanism used in a conventional facsimile apparatus.
In FIG. 9, an ink ribbon 51 is wound on a feed roll 52, and the leading end of the ink ribbon 51 is wound on a take-up roll 53. The take-up roll 53 turns in the direction of the arrow Y in the drawing. That is, the ink ribbon 51 advances in the direction of the arrow X in the drawing, being taken up on the take-up roll 53. The feed roll 52 and the take-up roll 53 are both supported nearly horizontally in relation to an unillustrated bottom plate of the facsimile apparatus by support frames 56A, 56B extending perpendicularly from the bottom plate.
The take-up operation of the ink ribbon 51 is effected by a friction mechanism 55 which drives the take-up roll 53. The friction mechanism 55 has a driving gear 58 which meshes with a gear 57 coaxially mounted on one end (on the right side in FIG. 9) of a spindle 53A of the take-up roll 53. To this driving gear 58 a specific driving effort is imparted. With the rotation of the driving gear 58, the take-up roll 53 turns in the direction of the arrow Y, taking up the ink ribbon 51. However, if the rotational speed of the driving gear 58 is fixed, the amount of the ink ribbon 51 taken up on the take-up roll 53 increases (namely, the take-up roll 53 taking up the ink ribbon 51 becomes larger in diameter), increasing the take-up speed of the ink ribbon 51. There occurs, therefore, a difference in rotational speed between the take-up roll 53 and an unillustrated platen roller for carrying recording paper. When a frictional force over a specific value is applied to the driving gear 58, or when the amount of the ink ribbon 51 wound on the take-up roll 53 has increased and the load to rotate the take-up roll 53 has increased over a specific value, the driving gear 58 idles to absorb the speed difference from the platen roller. The other end (the left side in FIG. 9) of the take-up roll 53 is rotatably supported on a bearing section 59 provided on a support frame 56A but no driving power is provided thereto.
Concurrently, on the left end of the feed roll 52 is provided a back tension mechanism 54. The back tension mechanism 54 has a driving gear 62 which is meshed with a gear 61 coaxially mounted on one end (the left side in FIG. 9) of a spindle 52A of the feed roll 52. A specific driving power is given to the driving gear 62. The end of the feed roller 52 on the opposite side of the back tension mechanism 54 is rotatably supported on a bearing 60 mounted on the support frame 56B, and is not provided with driving power.
With the provision of driving power to the driving gear 62, the back tension mechanism 54 gives a specific turning effort to the spindle 52A of the feed roll 52 in the direction of the arrow Z which is opposite to the direction of rotation of the take-up roll 53. Then, a force in the direction of feed (the direction of the arrow X) from the friction mechanism 55 and a force in the reverse direction (the opposite direction of the arrow X) of feed from the back tension mechanism 54 act on the ink ribbon 51.
As the friction mechanism 55 and the back tension mechanism 54 operate, the ink ribbon 51 is held with a fixed tension between the feed roll 52 and the take-up roll 53, thereby preventing the ink ribbon 51 from being broken and going slack.
In the conventional ink ribbon feed mechanism, however, the friction mechanism 55 and the back tension mechanism 54 are positioned on opposite sides, in the direction of travel (the direction of the arrow X), of the ink ribbon 51. That is, as shown in the plan view of FIG. 9, the friction mechanism 55 and the back tension mechanism 54 are arranged in diagonal positions of the wide ink ribbon 51. For example, the friction mechanism 55 is disposed on the right side, while the back tension mechanism 54 is on the left side. Therefore, when the ink ribbon 51 is taken up, the driving power from the friction mechanism 55 for taking up the ink ribbon 51 and the driving power from the back tension mechanism 54 are on the opposite end of the ink ribbon 51 and a twisting force is applied to the ink ribbon 51, producing a crease in the ink ribbon 51. A crease, if found in the ink ribbon 51, deteriorates or destabilizes the print quality.
Furthermore, since the driving mechanism and the gear mechanism are disposed on opposite sides of the ink ribbon 51, the ink ribbon feed mechanism itself increases in width. This destroys the goal of saving space.